Electrophysiological properties of fast (medial gastrocnmius) and slow (soleus) alpha motoneurons were examined with intracellular electrodes following section and/or reinnervation of the muscle nerves in the cat. The difference in properties between the two types of motoneurons became less prominent after chronic section of the muscle nerves (axotomy). The original properties of these motoneurons were restored following reinnervation of the muscle nerves. The degree of restoration of the motoneuron properties was closely related to the degree of motor reinnervation of the muscle whether or not the motoneuron had functional motor connections. It is concluded (1) that axotomy leads to dedifferentiation of the motoneuron properties, (2) that the dedifferentiated motoneuron properties by axotomy are redifferentiated following motor reinnervation and (3) that the primary signal for restoration of the motoneuron properties originates from the muscle, depending on the state of the muscle. These results suggest the presence of inductive functions exerted in the direction from muscle to motoneuron as well as in the converse direction.